1. Field of the Invention
The invention relates to a method for preventing or retarding the formation of gas hydrates or for reducing the tendency of such hydrates to agglomerate during the transport of a fluid comprising water and a hydrocarbon through a conduit, and, more particularly, to the addition to the fluid of a blend of a low molecular weight vinyl caprolactam polymer, or copolymers thereof, which are preferably made and applied in a suitable solvent, and a polyoxyalkylenediamine, to inhibit such gas hydrate formation.
2. Description of the Prior Art
It is well known in the art that the formation of gas hydrates in a conduit, e.g. a pipeline, during the transport of liquids, such as oil, and gases, particularly lower hydrocarbons, e.g. methane, ethane, propane, butane, isobutane and natural gas is a serious problem, especially in areas with a low temperature in the winter season or in the sea. Generally the temperatures are so low that gas hydrate formation, due to the inevitable presence of co-produced water in the wells takes place, if no special steps are taken. Insulation decreases the chance of gas hydrate formation; however, if the field is relatively small and far away from the production platform, the costs of using insulation are too high to make such field economically attractive. It is also known to add anti-freeze compounds, for example, glycol or methanol, during transport to minimize gas hydrate formation; however, large quantities of these compounds are required to be effective which is expensive. Alkyl glycosides also have been used for this purpose.
A representation of the prior art in this field are the following U.S. Pat. Nos. 4,915,176; 5,420,370; 5,432,292; 5,723,524; and 5,741,758; EPA 0526929A1; EPO 0323774A1; Can. Pat. Appln 2,073,577; WO 93/25798; WO95/17579; Gas Hydrates and Hydrate Prevention 73 GPA Annual Convention, pgs 85-93; WO 96/108456; WO 96/108636; WO 93/25798; EPA 0457375and WO 9412761.
The poly(vinyl caprolactam) (PVCL) described in U.S. Pat. No. 5,723,524 was synthesized in isopropanol and had an average molecular weight of 36,000 amu, as determined using size exclusion chromatography, otherwise known in the art as gel permeation chromatography (GPC, polyethylene glycol as standard).
The polyoxyalkylenediamines described in U.S. Pat. No. 5,741,758 was considered a more effective kinetic inhibitor than commercially available GAFFIX.RTM. VC-713 (International Specialty Products), a terpolymer of vinyl caprolactam/polyvinylpyrrolidone/dimethylaminoethyl methacrylate having an average molecular weight of approximately 200,000, or PVP (International Specialty Products), polyvinylpyrrolidone.